1. Field of the Invention
This invention relates to lithium/lithium ion batteries. It further relates to cyanoethylated additives that improve the performance of those batteries.
2. Description of the Prior Art
Essentially, all rechargeable batteries consist of several cells which in turn contain a cathode, an anode, and an ion carrying electrolyte. Usually, the electrolyte is a liquid and the anode and cathode are solids. In lithium polymer batteries (lithium batteries), the electrolyte is either a pure solid or a gel. The advantages of using a polymer solid or gel as electrolyte in batteries include (1) shape flexibility, (2) amenability to miniaturization, (3) extremely high surface to volume ratio, and so on.
Lithium battery technology is relatively new compared to that of conventional types such as the lead-acid battery and the nickel-cadmium battery. These conventional batteries contain aqueous electrolyte systems. Their practical energy density, measured in Wh/kg, is about 25 to 35 and about 35, respectively, which amounts to 1/8 and 1/7 of their theoretical density. In contrast, the lithium batteries have a practical energy density of about 120 Wh/kg, which amounts to 1/4 of their theoretical density. They are more efficient than the liquid electrolyte types and they can be useful at higher temperatures, i.e., up to 100.degree. C., as opposed to 50.degree. or less for the other types.
Power and energy generation in lithium batteries involves the shuttling of lithium ions through the electrolyte in contrast to the two other types of batteries in which the electrolyte participates in the battery reactions. Further, the problems associated with electrolyte leakage is either minimized or eliminated in the lithium batteries. Yet, in spite of all their advantages, lithium batteries have not reached the commercial market due mainly to the very low room temperature ionic conductivity of the polymer electrolyte, the high interfacial transfer resistance, and the electrolyte/electrode interfacial resistance. Several approaches are being pursued to improve these properties. While these approaches attempt to increase the bulk ionic conductivity of the electrolyte, very little attention is being paid to concurrently decrease the interfacial charge transfer resistance (R.sub.ct) and increase the interfacial stability. In a cell, both the electrolyte bulk ionic resistance and R.sub.ct are connected in series (in an equivalent circuit).
It is therefore an object of this invention to decrease the sum of the electrolyte bulk ionic resistance and the interfacial charge transfer resistance, as opposed to decreasing one and not the other.
Another object is to decrease the power losses in lithium batteries that is caused by the interfacial charge transfer resistance.
A further object is to make possible the design of lithium batteries that are lighter and more compact and yet can produce more power than the batteries of the art.
Additional objects, advantages, and novel features of the invention will become apparent to those skilled in the art upon examination of the following description or will be learned by practice of the invention.